The present invention relates generally to the field of hazardous waste containment facilities and more particularly to a system for forming a barrier to the liquid transport of hazardous waste contaminants within an aggregate particulate substrate.
The environment is plagued by the specter of hazardous waste plumes migrating through subsurface regions of the earth toward the underground water supplies. These plumes of hazardous waste are generated by a variety of sources including spills from trains or trucks, and waste storage facilities which have rusted through and are leaking a myriad of noxious substances into the soil.
Remediation measures are designed to minimize any harm which may be caused by these toxic wastes advancing through the earth toward the ground water level and remove the offending matter, if possible. The types of waste include radioactive wastes, carcinogens, organic solvents and heavy metals to name a few. The action taken to prevent catastrophic contamination of the environment varies according to the corresponding cleanup requirements for the contaminants.
One type of system extracts volatile wastes by placing vertical wells into the middle of the toxic waste plume and extracting any volatile gasses or liquids which are at the level of the well. An example of a system for the removal of volatile liquid contaminant is described in U.S. Pat. No. 4,660,639 to Visser, et al. ("Visser").
In Visser contaminants in the vadose zone with a low vapor pressure are volatized and then the resultant gases are removed. There is no guarantee that all of the volatile contaminant will be removed since the well operates from within the center of the plume of contaminants. Also, there is no provision for halting the spread of non-volatile liquids or for compensating for increased contaminant flow caused by an emergency, such as the unexpected breach of a waste storage tank.
Systems which pump out some of the contaminants that are in the immediate vicinity of the well do not provide a continuing reliable means for halting the spread of the toxic plume and act more as an after the fact solution. U.S. Pat. No. 4,832,122 to Corey, et al. ("Corey") teaches a system for removal of volatile contaminants from beneath the water table. Corey discusses a system in which a volatilizing substance is injected underneath the toxic waste plume and the resultant vapors or liquids are collected after they have passed up through the waste. The extraction and injection wells are located on either side of a contaminant plume that has crossed into the water table. The injection well of Corey is located within the saturated zone in the water table. The fluid, which is used by Corey, must be specific to removal of the contaminants in the plume and there is no barrier formed to stop the general liquid transport of contaminants.
Neither Corey or Visser are suitable for preventing ground water contamination due to water borne radioactive wastes such as are found at a waste storage site in Hanford, Wash., The site consists of a tank farm with single wall waste storage tanks used to hold radioactive nuclear wastes. These storage tanks have passed their operational life expectancy and many are now leaking radioactive wastes into the ground above the water table which feeds into the Columbia river basin. Because these wastes are physically as well as radioactivity "hot", water is continually added to the tanks which speeds up the plume's migration through the ground.
Systems designed for removal of volatile wastes from the vadose zone or the water table are not suitable to stop the approaching disaster represented by the Hanford site. In order to ensure the safety of the environment the plume must be stopped, i.e., a reliable barrier to further liquid transport of the radioactive waste must be installed.
At some sites another general technique is used in which an extensive grout barrier is constructed underneath the hazardous waste to prevent further spread of the plume toward the water table. Systems, such as the grout barrier, involve movement of a large amount of material at great expense, as well as, complex construction techniques. Further, the installation of these systems may require personnel down in a caisson to monitor construction.
The physical barriers, such as the grout barriers, serve as a preventive solution to block further contamination but have the disadvantage of being costly, difficult to build, sometimes dangerous for the workers and requiring the removal of large amounts of material during excavation. Further, in case of seismic events, such as earthquakes, the grout barrier can crack and break resulting in leakage of the contaminants through the grout barrier.
There have been no effective preventative measures which are low cost and take advantage of existing construction techniques and even existing facilities to provide a reliable line of defense to advancing contamination rather than try to undo regions which have already been contaminated.